implement error return tracing in the self-hosted compiler

[andrewrk]

Error Return Traces

fn zirErrorReturnTrace(
 sema: *Sema,
 block: *Block,
 extended: Zir.Inst.Extended.InstData,
) CompileError!Air.Inst.Ref {
 const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
 return sema.fail(block, src, "TODO: Sema.zirErrorReturnTrace", .{});
}